tion; see p. 165). They represent distinct entities, which have been referred to as 'solitary T-cell pseudolymphoma' in the literature [36,37]. These lesions are frequently located on the breasts of adult women (Fig. 20.7). Histology reveals a band-like infiltrate in an expanded papillary dermis, sometimes with exocytosis of lymphocytes within the epidermis (Figs 20.8 & 20.9). In several patients, a monoclonal rearrangement of the TCR genes has been reported. Some of the cases reported in the past as 'unilesional' or 'solitary' mycosis fungoides may represent examples of solitary T-cell pseu-dolymphoma but at present it is not possible to establish with certainty whether they are wholly benign monoclonal lymphoid proliferations or represent a variant of cutaneous T-cell lymphoma with a very favourable course . Surgical excision results in complete remission; recurrences are uncommon.
There may be some overlap between solitary T-cell pseu-dolymphoma and so-called lichenoid keratosis (see below).
Lichenoid (lymphomatoid) keratosis is a benign epithelial neoplasm, related in some cases to seborrhoeic keratosis and lentigo actinica (Fig. 20.10) [39,40]. Patients are elderly adults with small scaly plaques located usually on the trunk. The histopathological features with dense band-like inflammatory lymphoid infiltrates and often epidermotropism of lymphocytes may be indistinguishable from those of mycosis fungoides (Fig. 20.11) . Moreover, clonality of T lymphocytes can sometimes be found in these lesions. Accurate clinicopathological correlation is crucial to establish a correct diagnosis.
Differentiation of lichenoid (lymphomatoid) keratosis from solitary T-cell pseudolymphoma may be impossible in cases that do not show clear-cut features of an epithelial neoplasm, and the two conditions may be strictly related (see above).
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